Chapter Summary
Chemical change is also called chemical reaction.
A new substance is formed after a chemical reaction.
A chemical equation is written by using symbols of elements and molecules.
Zn + H2SO4 → ZnSO4 + H2
A complete chemical equation shows the reactants, products and their physical states symbolically.
A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation.
Balanced equation obeys the Law of Conservation of Masses.
Combination Reaction: In this reaction, two or more substances combine to form a new single substance.
C + O2 → CO2
Decomposition Reaction: In this reaction, a single substance decomposes to give two or more substances.
CaCO3 → CaO + CO2
Exothermic Reaction: Heat is evolved in this reaction.
C + O2 → CO2 + Heat
Endothermic Reaction: Heat is absorbed in this reaction.
CaCO3 + Heat → CaO + CO2
In this reaction, an element displaces another element from its compound.
CuSO4 + Fe → FeSO4 + Cu
Double Displacement Reaction: In this reaction, two different atoms or ions are mutually exchanged.
HCl + NaOH → NaCl + H2O
Oxidation: Gain of oxygen or loss of hydrogen is called oxidation.
C + 2HgO → CO2 + 2Hg
Reduction: Gain of hydrogen or loss of oxygen is called reduction.
HCl + NaOH → NaCl + H2O